Accuracy assessment of TDRSS-based TOPEX/Poseidon orbit determination

Orbit determination results are obtained for the Ocean Topography Experiment (TOPEX)/Poseidon spacecraft by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) using a batch-least-squares estimator available in the Goddard Trajector Determination System (GTDS) to process Tracking and Data Relay Satellite (TDRS) System (TDRSS) measurements. The GTDS orbit solutions are compared with the definitive Precision Orbit Determination (POD) orbit solutions. The root-mean-square (RMS) solution difference in the radial component is 28 centimeters.     

基于机动力模型的GEO卫星恢复期间定轨

北斗卫星导航系统(BDS)中GEO卫星频繁的轨道机动对高精度、实时不间断的导 航服务需求提出了更高要求, 如何在短弧跟踪条件下提高GEO卫星轨道快速 恢复能力, 是提升导航系统服务精度的关键因素. 针对该问题, 本文提出了基 于机动力模型的动力学定轨方法, 尝试利用高精度的C波段转发式测距数据, 辅 以机动期间的遥测遥控信息建立机动力模型, 联合轨控前后的观测数据进行动 力学长弧定轨. 利用BDS中GEO卫星实测数据进行了定轨试验与分析, 结果表明, 恢复期间需要采用解算机动推力的定轨方法, 联合机动前、机动期间和机 动后4h数据定轨的轨道位置精度在20m量级, 径向精度优于2.5m. 该方 法克服了短弧跟踪条件下动力学法定轨和单点定位中的诸多问题, 提供了解决 GEO卫星机动后轨道快速恢复问题的技术方法.      

Survey-only optical strategies for cataloguing space debris objects in the future European space surveillance system

In the framework of a potential European Space Situational Awareness System (ESSAS), we propose some optical strategies such that try to minimize the requirement of tracking measurements for the orbit determination computation when the catalogue is under construction. We will analyse them in terms of coverage, timeliness and orbit determination accuracy by means of the AS4 simulator (developed by Deimos Space S.L.U.). Moreover, observation campaigns have been performed from La Sagra Observatory in order to check the applicability of those strategies. These strategies are used for defining different choices for the future European Optical Space Surveillance System in the framework of the ESA contract no. 22738/09/D/HK.     

北斗卫星导航系统实时定轨与钟差处理策略

目前鲜有对北斗卫星导航系统（BeiDouNavigationSatelliteSystem,BDS）实时精密定轨与钟差确定的研究,文章提出了BDS实时轨道与实时钟差处理策略,包括了观测与动力学模型、实时轨道与实时钟差处理流程与评估方法。尤其对于实时钟差,为了提高计算效率,联合使用两个独立并行的线程估计非差绝对钟差和历元间相对钟差。利用多模全球卫星导航系统试验(MGEX)与全球连续检测评估系统（iGMAS）实测数据进行了北斗实时轨道与钟差解算,BDS实时轨道径向平均精度对于GEO卫星优于20cm,对于IGSO与MEO一般优于10cm;钟差精度对于GEO卫星为0.5~4.5ns,对于IGSO／MEO为0.2~2.0ns。基于目前的轨道与钟差结果,实时精密单点定位（PrecisePointPositioning,PPP）结果可以达到分米量级。     

基于光学测角数据的风云四号同步轨道卫星精密定轨

针对风云四号同步卫星的精密定轨和精度评估需求,首先利用地面光学测角数据对FY-4A卫星进行精密定轨,定轨后方位角和高度角的残差rms分别为0.25＂和0.45＂。与基于测距数据的轨道相比,位置精度在有测角数据的弧段内小于50m。进一步联合测角数据和测距数据对FY-4A卫星进行联合定轨,定轨后轨道重叠精度优于15m。利用联合定轨结果评估了基于测距数据的实时轨道产品精度,可以明显发现轨道精度随着测距数据的积累而逐步提高。     

Overview of TDRSS

The National Aeronautics and Space Administration (NASA) has developed the Tracking and Data Relay Satellite (TDRS) System (TDRSS) for operational tracking and communications support of low Earth-orbiting satellites. TDRSS currently consists of five geosynchronous spacecraft and the White Sands Complex (WSC) at White Sands, New Mexico. The Bilateration Ranging Transponder (BRT) System (BRTS) supports range and Doppler measurements for each TDRS using standard user tracking services. These measurements are used to generate well-determined ephemerides for the TDRSs. TDRSS provides S-band and Ku-band services through the single access (SA) antennas and S-band services through the S-band multiple access (SMA) phased array. TDRSS is capable of supporting coherent range and two-way Doppler tracking as well as noncoherent one-way return-link and one-way forward-link Doppler tracking of user spacecraft. Accurate one-way return-link tracking, which can use SMA, the most available TDRSS resource, requires a stable oscillator onboard the user spacecraft as the source of frequency. Two-way and one-way return-link tracking measurements are used for ground orbit determination for navigation and precise positioning; one-way forward-link tracking is used for autonomous onboard navigation with achievable accuracies better than those of the Global Positioning System (GPS) Precise Positioning System (PPS). This overview will discuss the various tracking and navigation capabilities of TDRSS, as well as many of the operational and research applications that have been conducted for missions such as Landsat-4, Ocean Topography Experiment (TOPEX)/Poseidon (T/P), Cosmic Background Explorer (COBE), and Extreme Ultraviolet Explorer (EUVE).     

“嫦娥4号”中继星任务轨道确定问题初探

"嫦娥4号"任务将采用着陆器、巡视器和绕飞地月拉格朗日L2点中继星进行月球背面的探测,中继星已先期发射,进入环绕地月L2点的晕(Halo)轨道。在中继星使命轨道动力学模型的基础上,通过相关仿真工作,开展了中继星在Halo轨道上的摄动源量级及影响定轨预报的主要因素分析,结果表明:太阳光压摄动是其主要影响因素。为降低其相关影响,提高定轨精度,在太阳光压球模型的基础上,结合中继星在轨运行特点及其星体结构特点,提出了一种求解光压等效面积的方法。经仿真分析,使用修正后的太阳光压球模型进行定轨求解,速度精度可提升约一个量级。     

Precision orbit determination for TOPEX/Poseidon using TDRSS doppler tracking data

Precision orbit determination on the TOPEX/Poseidon (T/P) altimeter satellite is now being routinely achieved with sub-5cm radial and sub-15 cm total positioning accuracy using state-of-the-art modeling with precision tracking provided by a combination of: (a) global Satellite Laser Ranging (SLR) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), or (b) the Global Positioning System (GPS) Constellation which provides pseudo-range and carrier phase observations. The geostationary Tracking and Data Relay Satellite System (TDRSS) satellites are providing the operational tracking and communication support for this mission. The TDRSS Doppler data are of high precision (0.3 mm/s nominal noise levels). Unlike other satellite missions supported operationally by TDRSS, T/P has high quality independent tracking which enables absolute orbit accuracy assessments. In addition, the T/P satellite provides extensive geometry for positioning a satellite at geostationary altitude, and thus the TDRSS-T/P data provides an excellent means for determining the TDRS orbits. Arc lengths of 7 and 10 days with varying degrees of T/P spacecraft attitude complexity are studied. Sub-meter T/P total positioning error is achieved when using the TDRSS range-rate data, with radial orbit errors of 10.6 cm and 15.5 cm RMS for the two arcs studied. Current limitations in the TDRSS precision orbit determination capability include mismodeling of numerous TDRSS satellite-specific dynamic and electronic effects, and in the inadequate treatment of the propagation delay and bending arising from the wet troposphere and ionosphere.     

Orbit determination of BeiDou navigation satellite system maneuvered satellites based on instantaneous velocity pulses parameters

The BeiDou navigation satellite system (BDS) comprises geostationary earth orbit (GEO) satellites as well as inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites. Owing to their special orbital characteristics, GEO satellites require frequent orbital maneuvers to ensure that they operate in a specific orbital window. The availability of the entire system is affected during the maneuver period because service cannot be provided before the ephemeris is restored. In this study, based on the conventional dynamic orbit determination method for navigation satellites, multiple sets of instantaneous velocity pulses parameters which belong to one of pseudo-stochastic parameters were used to simulate the orbital maneuver process in the orbital maneuver arc and establish the observed and predicted orbits of the maneuvered and non-maneuvered satellites of BeiDou regional navigation satellite system (BDS-2) and BeiDou global navigation satellite system (BDS-3). Finally, the single point positioning (SPP) technology was used to verify the accuracy of the observed and predicted orbits. The orbit determination accuracy of maneuvered satellites can be greatly improved by using the orbit determination method proposed in this paper. The overlapping orbit determination accuracy of maneuvered GEO satellites of BDS-2 and BDS-3 can improve 2–3 orders of magnitude. Among them, the radial orbit determination accuracy of each maneuvered satellite is basically better than 1 m. simultaneously, the combined orbit determination of the maneuvered and non-maneuvered satellites does not have a great impact on the orbit determination accuracy of the non-maneuvered satellites. Compared with the multi GNSS products (indicated by GBM) from the German Research Centre for Geosciences (GFZ), the impact of adding the maneuvered satellites on the orbit determination accuracy of BDS-2 satellites is less than 9 %. Furthermore, the orbital recovery time and the service availability period are significantly improved. When the node of the predicted orbit is traversed approximately 3 h after the maneuver, the accuracy of the predicted orbit of the maneuvered satellite can reach that of the observed orbit. The SPP results for the BDS reached a normal level when the node of the predicted orbit was 2 h after the maneuver.     

基于固定模糊度PPP的低轨卫星实时精密定轨

传统动力学定轨法受制于动力学模型精度,传统几何定轨法精度受限,只能达到亚米级,而基于精密单点定位（PPP）模式的几何定轨法一般采用浮点解,定轨精度及可靠性较基于双差模式的相对定位较差。为提高PPP模式低轨定轨的定位性能,利用中国区域内外的IGS测站计算出当前所有卫星的宽巷和窄巷相位小数偏差产品,对经过中国大陆区域上空的国产低轨卫星海洋二号（HY-2）和资源三号 (ZY-3) 卫星进行固定模糊度PPP的定轨解算,与事后精密轨道结果进行比较,分析其外符合精度。结果表明：仅利用约10min弧段的HY-2和ZY-3卫星数据,切向与径向的定轨精度可达2cm左右,法向为5cm左右,较浮点解定轨精度大幅提升。基于固定模糊度PPP的定轨方法能够满足厘米级的实时精密定轨。     

Orbit determination of BDS-3 satellite based on regional ground tracking station and inter-satellite link observations

The BeiDou global navigation satellite system (BDS-3) has established the Ka-band inter-satellite link (ISL) to realize a two-way ranging function between satellites, which provides a new observation technology for the orbit determination of BDS-3 satellites. Therefore, this study presents a BDS satellite orbit determination model based on ground tracking station (GTS) observations and ISL ranging observations firstly to analyze the impact of the ISL ranging observations on the orbit determination of BDS-3 satellites. Subsequently, considering the data fusion processing, the variance component estimation (VCE) algorithm is applied to the parameter estimation process of the satellite orbit determination. Finally, using the measured data from China’s regional GTS observations and BDS-3 ISL ranging observations, the effects of ISL ranging observations on the orbit determination accuracy of BDS-3 satellites are analyzed. Moreover, the impact of the VCE algorithm on the fusion data processing is evaluated from the aspects of orbit determination accuracy, Ka-band hardware delay parameter stability, and ISL ranging observation residuals. The results show that for China’s regional GTSs, the addition of BDS-3 ISL ranging observations can significantly improve the orbit determination accuracy of BDS-3 satellites. The observed orbit determination accuracy of satellite radial component is improved from 48 cm to 4.1 cm. In addition, when the initial weight ratio between GTS observations and ISL ranging observations is not appropriate, the various indicators which include orbit determination accuracy, ISL hardware delay, and ISL observation residuals were observed to have improved after the adjustment of the VCE algorithm. These results validate the effectiveness of the VCE algorithm for the fusion data processing of the GTS observations and ISL ranging observations.     

ERS-1 and ERS-2 operational and precise orbit determination

This paper presents the European Space Operations Centre's orbit determination and prediction systems for the ERS-1 mission. The routine operational orbit determination and prediction subsystem is discussed briefly, and statistics of the accuracy compared to the requirements are given. The precise orbit determination subsystem is then described, and the accuracy of its results are compared to those of the operational orbit system and to the D-PAF preliminary orbit solutions. Some geophysical results from the altimeter data, processed in these orbit determinations, are also presented. The ESOC/OAD ‘ERS-1 Orbit Report’ is introduced as a document providing this information on a monthly basis. Finally, this paper describes how the experience gained with the precise orbit determination will be exploited to further improve the accuracy of the routine system that will be used for ERS-2, and provides an estimate of this accuracy.     

基于Gooding算法的天基光学目标跟踪定轨

开展了基于Gooding算法的400 km天基平台光学目标监测的轨道确定研究,当测量误差为3"和6"时,分别对800,1500及36 000 km轨道高度目标进行初始轨道确定及轨道改进分析.仿真结果表叽利用400 km轨道高度平台对800～1500 km轨道高度目标进行初定轨,测量数据误差为3"～6"时,4～15 mi...     

Analysis of BDS-3 distributed autonomous navigation based on BeiDou system simulation platform

Satellite autonomous navigation is an important function of the BeiDou-3 navigation System (BDS-3). Satellite autonomous navigation means that the navigation satellite uses long-term forecast ephemeris and Inter-Satellite Link (ISL) measurements to determinate its own spatial position and time reference without the support of the ground Operation and Control System (OCS) for a long time to ensure that the navigation system can normally maintain the time and space reference. This paper aims to analyze the feasibility of distributed autonomous navigation algorithms. For the first time, a ground parallel autonomous navigation test system (GPANTS) is built. The performance of distributed autonomous navigation is then analyzed using the two-way ISL ranging of BDS-3 satellites. First, the BDS simulation platform and the GPANTS are introduced. Then, the basic principles of distributed satellite autonomous orbit determination and time synchronization based on ISL measurements are summarized. Preliminary evaluation of the performance of the BDS-3 constellation autonomous navigation service under ideal conditions through simulation data. Then the performance of autonomous navigation for 22 BeiDou-3 satellites using ISL measurements is evaluated. The results show that when satellites operate autonomously for 50 days without the support of any ground station, the User Range Error (URE) of autonomous orbit determination is better than 3 m, and the time synchronization accuracy is better than 4 ns.     

联合北斗导航与星间链路的大椭圆卫星定轨方法

传统的地面测控和GNSS均无法实现HEO卫星全弧段的跟踪观测.在分析北斗导航信号及其星间链路信号对典型HEO的观测几何及覆盖特性的基础上,利用北斗导航及其星间链路对HEO测控支持形成互补的特点,提出了一种卫星导航与星间链路相结合的自主导航方法.对HEO定轨进行分段划分并基于EKF设计了卫星导航与星间链路数据融合定轨的自主导航算法.分析结果表明,本文提出的方法能够从全弧段上改善HEO的观测几何,定轨精度比仅使用卫星导航提高了2个数量级,并且仅需较少的星间链路资源.      

Impact of GPS antenna phase center variations on precise orbits of the GOCE satellite

The first European Space Agency Earth explorer core mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) has been launched on March 17, 2009. The 12-channel dual-frequency Global Positioning System receiver delivers 1 Hz data and provides the basis for precise orbit determination (POD) on the few cm-level for such a very low orbiting satellite (254.9 km). As a member of the European GOCE Gravity Consortium, which is responsible for the GOCE High-level Processing Facility (HPF), the Astronomical Institute of the University of Bern (AIUB) provides the Precise Science Orbit (PSO) product for the GOCE satellite. The mission requirement for 1-dimensional POD accuracy is 2 cm. The use of in-flight determined antenna phase center variations (PCVs) is necessary to meet this requirement. The PCVs are determined from 154 days of data and the magnitude is up to 3-4 cm. The impact of the PCVs on the orbit determination is significant. The cross-track direction benefits most of the PCVs. The improvement is clearly seen in the orbit overlap analysis and in the validation with independent Satellite Laser Ranging (SLR) measurements. It is the first time that SLR could validate the cross-track component of a LEO orbit.     

基于自适应滤波的编队卫星实时相对定轨

提出基于自适应滤波的编队卫星实时相对定轨算法,利用2005-12-09—10两颗GRACE（Gravity Recovery and Climate Experiment）卫星的GPS（Global Positioning System）实测数据进行实时相对定轨试验计算,采用JPL（Jet Propulsion Laboratory）轨道对试验结果外部检核,结果表明:①自适应滤波相对定轨通过自适应因子,可以较好地平衡编队卫星的观测信息和相对动力学信息,其相对定轨结果精度优于Kalman滤波相对定轨结果;②自适应滤波相对定轨结果随着星间基线缩短而精度提高;③两颗GRACE卫星采用单频伪距和广播星历进行自适应滤波相对定轨,可以得到精度优于6cm的星间基线。     

Higher order ionospheric error correction in BDS precise orbit determination

The ionospheric error affects the accuracy of the Global Navigation Satellite Systems observation and precise orbit determination. Usually, only the first order ionospheric error is considered, which can be eliminated by the ionospheric-free linear combination observation. But the remaining higher order ionospheric error will affect the accuracy of observations and their applications. In this paper, the influence of the higher order ionospheric error have been studied by using the International Geomagnetic Reference Field 13 and the Global Ionosphere Maps model produced by the Center for Orbit Determination in Europe. Focus on ionospheric error, the experiment of paper at doy 302 in 2019, which show that the second order ionospheric error impacting BeiDou Navigation Satellite System (BDS) B1I and B3I observation is 6.3569 mm and 11.8484 mm, respectively. Whereas, the third order ionospheric error impacting BDS B1I and B3I observation is 0.1734 mm and 0.3977 mm, respectively. Due to the current measurement accuracy of BDS carrier-phase observation can reach 2 mm, the influence of high order ionospheric error on observation should be considered. For BDS precise orbit determination, the orbit overlapping results are indicated that its orbit accuracy can be improved approximately 5 mm with the higher order ionospheric error correction, which is also in agreement with the results of Satellite Laser Ranging in this work.     

低轨飞行器利用GPS定轨的算法研究

详细讨论了低轨飞行器利用ＧＰＳ系统定轨的原理和方法。分析了低轨飞行器选星时应考虑的问题,并根据导航星及用户模型进行了选星试验;探讨了利用最小二乘法进行解算定轨;详细分析了卡尔曼滤波算法,针对低轨飞行器提出了一个九状态卡尔曼滤波模型,并在此基础上进行了仿真模拟计算。另外,根据用户对电源能量和可靠性的特殊要求,提出了一种比较实用的定轨方法。仿真结果表明,提出的方法在精度上满足用户的要求,适合于工程实际应用。     

基于GNSS测量的天宫二号质心确定

由于轨道机动燃料消耗,科学载荷加载、分离,以及伴飞小卫星在轨释放等原因引起天宫二号空间站质心(COM)发生位移,从而影响天宫二号的动力学质心定轨精度。针对这一问题,提出了基于全球导航卫星系统(GNSS)测量数据的简化动力学质心估计方法。燃料消耗是引起天宫二号质心发生位移的主要原因,质心在本体坐标系X轴方向位移最为显著。利用GNSS测量数据对天宫二号进行质心估计和精密定轨,在三轴对地稳定姿态下,本体坐标系X轴方向与轨道切向重合,定轨结果对本体坐标系X轴方向的质心位移并不敏感。但在连续偏航模式下,本体坐标系X轴在轨道法向上有较大分量,X轴方向的质心位移对基于GNSS测量计算的精密定轨结果有较大影响。定性和定量分析结果表明:偏航姿态模式下天宫二号本体坐标系X轴方向质心位移估计具有可行性。天宫二号实测数据计算结果表明:与未做质心估计的定轨结果进行对比,质心估计后表征轨道动力学建模误差的经验加速度补偿水平在轨道径向、切向和法向上分别降低62%、50%和65%;载波相位后验残差标准差降低0.04 cm;精密轨道与全球激光测距数据比较精度提高0.86 cm。所提方法可以应用于大型低轨航天器在轨质心估计。